Grain-Size Dependence of Thermal and Electrical Properties in (Cr,Mo,Ta,V,W)C1-δ High-Entropy Carbide Ceramics

Abstract

Thermal and electrical transport in high-entropy carbides can be influenced by grain-boundary scattering, but the relevant microstructural regime remains uncertain. Here, near-fully dense $(Cr,Mo,Ta,V,W)C_{1-δ}$ ceramics were densified by spark plasma sintering at 1750-1950 °C, producing average grain sizes from 9.3 $\pm$ 4.9 to 28.8 $\pm$ 15.3 $μ$m while retaining the rock-salt phase. Heat capacities were measured experimentally and estimated by the Neumann-Kopp law with the latter used to calculate thermal conductivity. Thermal conductivity values were in the range of 6.8-7.1 W $m^{-1}$ $K^{-1}$ at room temperature, but showed no systematic dependence on grain size within the investigated range. Room-temperature electrical resistivity values were in the range of 151.9 to 177.0 $μΩ$ cm and likewise showed no grain-size dependence. The electron contribution to room-temperature thermal conductivity was estimated to be approximately 58-68% of total thermal conductivity as estimated using the Wiedemann-Franz law and the theoretical Lorenz number. The results indicated that processing-induced grain coarsening did not produce clearly resolvable transport-property changes under the conditions investigated leading to the conclusion that intrinsic disorder and defect chemistry may exert stronger influences on properties.